a) Field of the Invention
The invention is directed to a method for introducing a treatment medium in the form of chemicals into the waste gas flow in combustion processes by means of a carrier medium through an atomizing nozzle for reducing the nitric oxide concentration.
b) Background Prior Art
In order to reduce the nitric oxide emissions, it is known to introduce chemicals into the hot waste gas flow, generally ammonia, sal ammoniac, urea or calcium cyanamide, which can be mixed under certain circumstances with different hydrocarbon compounds as so-called reinforcing chemicals. The introduction is effected at temperatures of at least 600.degree. C., wherein the most favorable possible uniform distribution of the chemicals is of decisive significance for an optimal running of the chemical reactions for bonding or reducing the nitric oxides. According to the current state of the art, the uniform distribution over the entire flue gas flow is achieved on the one hand by means of the arrangement of a plurality of nozzles along the cross section of the flue gas flue and on the other hand--and a particularly great importance is even attributed to this as a rule--by means of using two-component nozzles, steam or compressed air being supplied to the latter as atomizing medium. However, it is precisely the use of its own atomizing medium which has a number of disadvantages. Compressed air or steam are relatively expensive media, since they always require high amounts of energy and--in the case of steam--prepared evaporator feed water. The guidance of these media through lines until the individual nozzles proves to be costly, since either thermally insulated pipes must be used in the case of steam and/or relatively large pipe cross sections for reducing the pressure loss in the system. The expansion of the media at the nozzle outlet and the media flow in the lines generate a relatively high noise level which often even necessitates soundproofing. Further, it must also be taken into account that an unwanted dilution of the flue gases by air or steam reduces the efficiency of the steam production or possibly the waste gas cleaning system.
The use of two-component nozzles also brings about the disadvantage that the carrier medium which serves to atomize the treatment medium, i.e. the chemicals, must be used in large quantities, since the atomization is brought about due to kinetic energy of the carrier medium. Accordingly, a heavy dilution of the flue gases also occurs with small quantities to be atomized.
It is the object of the present invention to enable the introduction of a treatment medium, i.e. predetermined chemicals, such as ammonia, sal ammoniac, urea or calcium cyanamide into the flue gas with a high degree of efficiency, low expenditure of energy and low expenditure on construction.
This object is met, according to the invention, proceeding from a method of the type named in the beginning, in that the carrier medium is brought to a pressure level necessary for atomization and is supplied to an atomizing nozzle having a single nozzle opening, and in that the treatment medium, which is mixed with the carrier medium in any desired quantitative proportion immediately before exiting from the nozzle opening, is supplied to the atomizing nozzle, wherein the treatment medium is brought to the pressure level of the carrier medium prior to the mixing process.
By means of this method, it is possible to introduce any desired quantity of treatment media into the flue gas without operating the nozzle at different pressures and flow quantities, so that the nozzle constantly operates with the best efficiency. The quantity of treatment medium to be introduced is changed in that the ratio of carrier medium and treatment medium is variously adjusted prior to the atomization process. With the use of a one-component nozzle, operation can always be effected under the same conditions, in contrast to the two-component nozzles in which a reduction of the carrier medium was necessary when the quantity of treatment medium was reduced and in which an increase of the treatment medium necessarily required an increase of the carrier medium. Moreover, with the one-component nozzle, the atomization of the treatment medium is not effected on the basis of kinetic energy which must be applied by means of the carrier medium, but rather on the basis of the change in pressure prior to and subsequent to the nozzle opening, which leads to a substantial reduction of the carrier medium. This is necessary in order to operate the nozzle with a determined throughflow, regardless of the proportion and quantity of the treatment medium. Further, the carrier medium can serve to cool the atomizing nozzle when the atomization of the treatment medium is completely adjusted, this is when the treatment medium is set at the pressure of the carrier medium to provide complete atomization of the mixture out of the nozzle. In this case, as a result of the heating action in the furnace, the nozzle would be subject to impairments which are prevented by means of the atomization of the carrier medium.
According to a development of the invention, the quantity of added treatment medium can be adjusted as a function of the NO.sub.x gas concentration in the treated flue gas flow. The NO.sub.x gas concentration is thus measured in an area in which the treatment medium is already located and in which the corresponding chemical reaction has taken place.
However, the quantity of treatment medium can also be adjusted as a function of the waste gas quantity.
Further, the atomization pressure can be adjusted as a function of the waste gas quantity according to an advantageous embodiment of the invention.
In order to prevent excessive fluctuations in pressure in the overall system during the supply of treatment medium, it is advisable, in a further development of the invention, that the treatment medium be supplied to the atomizing nozzle in concentrated form, wherein the concentration is adjustable as a function of the required amount. In general, the concentration can be effected up to the respective solution limit of the treatment medium.
Ammonia, sal ammoniac, urea or calcium cyanamide, for example, can be used as treatment medium. In this treatment medium, it is advisable to use water as carrier medium.
The invention is explained in more detail in the following by means of the drawings.